Bathroom Exhaust Fan Question

First off, I live in Minnesota and bought my house this past summer. My bathroom did not have an exhaust fan. I was going to install one. Things got bust at work and I didn't have a chance to start it until this past fall. I got the fan/light installed and all of the electrical connected. My original plan was to vent out of the roof. We had rain for awhile and then a work project kept me from being able to install the roof vent.

Now that it's December, the person that was going to help me (not a contractor) said I need to wait until spring due to the cold weather.

Is it best to wait until spring? My concern was that even not running the fan, some moisture will get into the attic.

I have vented soffits by my bathroom so I figured using one of those vents, even temporarily was a bad idea. Thanks.